In a recent navigation system, an HDD (Hard Disk Drive) becomes the main current as a storage medium of map information, and the storage capacity of data increases year by year, thereby increasing retainable map information (facility information, road information and the like) as well. Thus, it becomes possible to store various useful information besides the map information in advance to provide information convenient for a user.
As one of onboard apparatuses, a broadcast receiver is known. The broadcast receiver is mounted on a vehicle and operates thereon. Accordingly, a state can occur in which a broadcast wave received state becomes worse depending on the position of the vehicle. Thus, a technique has been developed which notifies a user of the broadcast wave received state. For example, as for an onboard radio receiver that automatically switches to a traffic information broadcast even though it is tuned at present to another broadcasting station or a source, Patent Document 1 discloses a radio receiver that inhibits an alarm operation or automatic search in the case of temporary reduction in electric field strength such as when passing through a tunnel.
In addition, Patent Document 2, considering a case where an onboard FM multiplex broadcast receiving device sometimes cannot display information given by an FM multiplex broadcast even though it can output sounds of the FM broadcast because of weak electric field in a bad receiving condition such as when it moves to a place in a bad receiving condition, discloses an FM multiplex broadcast receiving device capable of notifying a user of a reason for the difficulty of displaying although the sounds are audible.